Method and system of channel adaptation

ABSTRACT

The present invention relates to transmissions and retransmissions in a communications system. It reveals a method and system for backward compatible detection of an introduced channel sub-frame structure particularly well suited for data transmissions. The invention is well suited for a cellular mobile radio communications system, particularly a Universal Mobile Telecommunications System, UMTS.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to transmissions and retransmissions in acommunications system, and more especially it relates to a cellularmobile radio system, particularly to a Universal MobileTelecommunications System, UMTS or WCDMA system.

BACKGROUND AND DESCRIPTION OF RELATED ART

Transmission and retransmission of data to or from a mobile station, MS,or user equipment, UE, is previously known. It is also known to usemedium access control and radio link control layers of a UMTS protocolstructure in acknowledged mode for dedicated channels.

In acknowledged mode, retransmissions are undertaken in case of detectedtransmission errors not recovered by forward error control. This is alsocalled automatic repeat request, ARQ. With ARQ, retransmissions can beundertaken unless a transmitted message is (positively) acknowledged orif it is negatively acknowledged. Generally there are time limits forthe respective positive and negative acknowledgements to be considered.

Within this patent application, a radio network controller, RNC, isunderstood as a network element including a radio resource controller.Node B is a logical node responsible for radio transmission/reception inone or more cells to/from a User Equipment. A base station, BS, is aphysical entity representing Node B.

Medium access control, MAC, and radio link control, RLC, is used withinradio communications systems like General Packet Radio Services, GPRS,and UMTS.

With reference to FIG. 1, Node B1 and Node B2 of a radio communicationssystem are logical nodes responsible for radio transmission/reception inone or more cells to/from the User Equipment UE. BS1 and BS2 arephysical entities representing Node B1 and Node B2 respectively. Node B1and Node B2 terminate the air interface, called Uu interface withinUMTS, between UE and respective Node B towards the radio networkcontroller RNC. In UMTS the interface between a Node B and an RNC iscalled Iub interface.

3^(rd) Generation Partnership Project (3GPP): Technical SpecificationGroup Radio Access Network, Physical Layer Procedures, 3G TS 25.301v3.6.0, France, September 2000, specifies in chapter 5 Radio InterfaceProtocol Architecture of a UMTS system. There are three protocol layers:

-   -   physical layer, layer 1 or L1,    -   data link layer, layer 2 or L2, and    -   network layer, layer 3 or L3.

Layer 2, L2, and layer 3, L3 are divided into Control and User Planes.Layer 2 consists of two sub-layers, RLC and MAC, for the Control Planeand four sub-layers, BMC, PDCP, RLC and MAC, for the User Plane. Theacronyms BMC, PDCP, RLC and MAC denote Broadcast/Multicast Control,Packet Data Convergence Protocol, Radio Link Control and Medium AccessControl respectively.

FIG. 2 illustrates a simplified UMTS layers 1 and 2 protocol structurefor a Uu Stratum, UuS, or Radio Stratum, between a user equipment UE anda Universal Terrestrial Radio Access Network, UTRAN.

Radio Access Bearers, RABs, make available radio resources (andservices) to user applications. For each mobile station there may be oneor several RABs. Data flows (in the form of segments) from the RABs arepassed to respective Radio Link Control, RLC, entities which amongstother tasks buffer the received data segments. There is one RLC entityfor each RAB. In the RLC layer, RABs are mapped onto respective logicalchannels. A Medium Access Control, MAC, entity receives data transmittedin the logical channels and further maps logical channels onto a set oftransport channels. In accordance with subsection 5.3.1.2 of the 3GPPtechnical specification, MAC should support service multiplexing e.g.for RLC services to be mapped on the same transport channel. In thiscase identification of multiplexing is contained in the MAC protocolcontrol information.

Transport channels are finally mapped to a single physical channel whichhas a total bandwidth allocated to it by the network. In frequencydivision duplex mode, a physical channel is defined by code, frequencyand, in the uplink, relative phase (I/Q). In time division duplex mode aphysical channel is defined by code, frequency, and time-slot. The DSCH,e.g., is mapped onto one or several physical channels such that aspecified part of the downlink resources is employed. As furtherdescribed in subsection 5.2.2 of the 3GPP technical specification the L1layer is responsible for error detection on transport channels andindication to higher layer, FEC encoding/decoding andinterleaving/deinterleaving of transport channels.

PDCP provides mapping between Network PDUs (Protocol Data Units) of anetwork protocol, e.g. the Internet protocol, to an RLC entity. PDCPcompresses and decompresses redundant Network PDU control information(header compression and decompression).

For transmissions on point-to-multipoint logical channels, BMC stores atUTRAN-side Broadcast Messages received from an RNC, calculates therequired transmission rate and requests for the appropriate channelresources. It receives scheduling information from the RNC, andgenerates schedule messages. For transmission, the messages are mappedon a point-to-multipoint logical channel. At the UE side, BMC evaluatesthe schedule messages and deliver Broadcast Messages to upper layer inthe UE.

3G TS 25.301 also describes protocol termination, i.e. in which node ofUTRAN the radio interface protocols are terminated, or equivalently,where within UTRAN the respective protocol services are accessible.

3^(rd) Generation Partnership Project (3GPP): Technical SpecificationGroup Radio Access Network, Physical Layer Procedures, 3G TS 25.322v3.5.0, France, December 2000, specifies the RLC protocol. The RLC layerprovides three services to the higher layers:

-   -   transparent data transfer service,    -   unacknowledged data transfer service, and    -   acknowledged data transfer service.

In subsection 4.2.1.3 an acknowledged mode entity, AM-entity, isdescribed (see FIG. 4.4 of the 3GPP Technical Specification). Inacknowledged mode automatic repeat request, ARQ, is used. The RLCsub-layer provides ARQ functionality closely coupled with the radiotransmission technique used.

3^(rd) Generation Partnership Project (3GPP): Technical SpecificationGroup Radio Access Network, Physical channels and mapping of transportchannels onto physical channels (FDD), 3G TS 25.211 v4.6.0, France,September 2002, describes characteristics of the Layer 1 transportchannels and physicals channels in the FDD mode of UTRA. Chapter 4describes dedicated and common transport channels, such as

-   -   Dedicated Channel, DCH;

Broadcast Channel, BCH;

-   -   Forward Access Channel, FACH;    -   Paging Channel, PCH;    -   Random Access Channel, RACH;    -   Common Packet Channel, CPCH; and    -   Downlink Shared Channel, DSCH.

Chapter 5 defines a radio frame and a slot on the physical channelaccording to the 3GPP technical specification:

-   -   A radio frame is a processing duration, which consists of 15        slots. The length of a radio frame corresponds to 38400 chips.    -   A slot is a duration, which consists of fields containing bits.        The length of a slot corresponds to 2560 chips.

The specification defines two uplink dedicated physical channels:

-   -   uplink Dedicated Physical Data Channel, uplink DPDCH; and    -   uplink Dedicated Physical Control Channel, uplink DPCCH.

The 3GPP technical specification explains,

-   -   “The uplink DPDCH is used to carry the DCH transport channel.        There may be zero, one, or several uplink DPDCHs on each radio        link.    -   The uplink DPCCH is used to carry control-information generated        at Layer 1. The Layer 1 control information consists of known        pilot bits to support channel estimation for coherent detection,        transmit power-control (TPC) commands, feedback information        (FBI), and an optional transport-format combination indicator        (TFCI). The transport-format combination indicator informs the        receiver about the instantaneous transport format combination of        the transport channels mapped to the simultaneously transmitted        uplink DPDCH radio frame. There is one and only one uplink DPCCH        on each radio link.”

FIG. 3 illustrates the frame structure for uplink DPDCH and DPCCH. Indownlink direction DPDCH and DPCCH are time division multiplexed.

The frame structure of uplink data and control parts associated withCPCH is similar to that of uplink DPDCH and uplink DPCCH respectively.

3^(rd) Generation Partnership Project (3GPP): Technical SpecificationGroup Radio Access Network, Multiplexing and channel coding (FDD), 3G TS25.212 v5.0.0, France, March 2002, describes the characteristics of theLayer 1 multiplexing and channel coding in the FDD mode of UTRA. Section4.3 describes transport format detection. For a Coded CompositeTransport Channel (CCTrCH), if the transport format set, TFS, of aTransport Channel, TrCH, contains more than one transport format, thetransport format can be detected either by signaling the particulartransport format using the TFCI field, by blindly detecting thetransport format by use of channel decoding and CRC check or usingguided detection from at least one other guiding TrCH.

3^(rd) Generation Partnership Project (3GPP): Technical SpecificationGroup Radio Access Network, Radio Resource Control (RRC), ProtocolSpecification, 3G TS 25.331 v4.7.0, France, September 2002, specifiesthe RRC protocol for the UE-UTRAN interface. Section 10.3.5.11 describesin tabular format Transport Channel, TrCH, Information Elements of RRCmessages related to semi-static transport format information, TFI,including transmission time interval, TTI. TTI is the duration of dataover which coding and interleaving is performed for a certain transportchannel. According to the 3GPP technical specification, TTI is one of10, 20, 40 and 80 ms. Section 10.3.5.80 describes transport formatcombination, TFC, control duration, defining a period in multiples of 10ms frames for which the defined TFC sub-set is to be applied. Section10.3.6.81 describes a Transport Format Combination Indicator, TFCI,combining indicator, indicating by TRUE or FALSE whether a part of TFCI,TFCI2, should be softly combined with other TFCI2 parts of the combiningset. Section 10.3.6 describes corresponding Physical Channel, PhyCH orPhCH, Information Elements as applicable.

None of the cited documents above discloses a method and system ofcompatibly extending an existing channel structure for the radiointerface adapting a static or semi-static transmission interval suchthat alternating TTI could be adopted to a data channel. Further, it isnot revealed a method and system such that whether or not this extensionis made use of could be blindly detected, not requiring additionalsignaling.

SUMMARY OF THE INVENTION

WCDMA and UMTS presently only supports TTIs of 10, 20, 40 or 80 ms.According to prior art, one TFCI is normally transmitted in each radioframe, i.e. once every 10 ms.

Delay problems have been identified for existing channel structure insome situations, e.g. communications according to TCP (TransmissionControl Protocol), at high data rates, particularly in the uplinkbetween UE and Node B.

Further, transmission power restrictions, particularly in uplinkdirection makes introduction of additional transport formats to be codemultiplexed unfavorable, if not impossible.

Consequently, it is an object of this invention to introduce a backwardcompatible channel structure allowing for shorter than existingtransmission time intervals without PAR (peak-to-average power ratio)increase.

A further object is to introduce a channel structure allowing forinterchanging transmissions of radio frame structured data and sub-framestructured data, respectively.

It is also an object to introduce a sub-frame structure, the applicationof which may be detected without explicit signaling, in terms oftransmission of additional symbols.

Finally it is an object to present an explicit method and system fordetection of whether a sub-frame channel structure is applied or not.

Preferred embodiments of the invention, by way of examples, aredescribed with reference to the accompanying drawings below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows communication, according to the invention, between a UE anda base station involved in a connection between an RNC and the UE.

FIG. 2 displays a layered protocol structure, according to prior art, ina radio communications system.

FIG. 3 illustrates the frame structure for uplink DPDCH and DPCCH,according to prior art.

FIG. 4 shows a preferred frame and sub-frame channel structure for DPDCHand DPCCH, according to the invention.

FIG. 5 displays a layered protocol structure, according to theinvention, in a radio communication system.

FIG. 6 shows a flow chart schematically illustrating detection accordingto a preferred embodiment of the invention.

FIG. 7 shows a flow chart schematically illustrating detection accordingto an alternative embodiment of the invention.

FIG. 8 schematically illustrates MAC and RLC protocol layers in amultilayer protocol structure.

DESCRIPTION OF PREFERRED EMBODIMENTS

WCDMA and UMTS presently only supports TTIs of 10, 20, 40 or 80 ms.Normally, one TFCI is transmitted in each radio frame, i.e. once every10 ms. In this patent application particular radio frame TFCI is alsoreferred to as TFCI_(rf), to distinguish from particular sub-frame TFCI,referred to as TFCI_(sf). In case of TTIs being integer multiples of 10ms, the same TFCI content is repeated in the multiple radio frames foradditional redundancy to be combined for increased reliability. Aplurality of transport channels are generally multiplexed and coded intoa Coded Composite Transport Channel, CCTrCH, for transmission on thephysical channel. There is one TFCI for each CCTrCH. According to priorart, TTI is fixed for a particular TrCH.

Excessive delay may cause problems to e.g. TCP (Transmission ControlProtocol).

Consequently, a problem with substantial delays of data transmissions isidentified. A solution to the problem to be applied in e.g. UMTS or aWCDMA system should be backward compatible with equipment operatingaccording to existing specifications. Such backward compatibility willprovide for soft handover possibility also between Nodes B operatingaccording to different releases and non-increased power requirement onUE at cell border. Further, for prior art 3GPP specifications there is arestriction from e.g. existing Release'99 as there is no means toindicate different TTIs for a TrCH.

A different TTI could be achieved by setting up a new code multiplexeddata channel. However, this would require use of more than one code withan inherent risk of increasing PAR (peak-to-average power ratio), whichis a problem particularly in uplink direction, predominantly due topower limitation of user equipment, UE.

A further problem is RRC signaling according to prior art requiring 40ms TTI. One rationale for this interval is strict power budgets of UE tobe kept also at cell border.

According to the invention the above mentioned problems are solved byintroducing an alternative transmission time interval, and acorresponding sub-frame, shorter than that existing, requiring a newstructure on the physical channel. A channel structure is superimposedon an existing channel structure to allow use of shorter TTIs onexisting data channels, DPDCHs, without violating existing data channelTTI structure and without increasing PAR.

The smaller block size obtained will both increase likelihood of correcttransmission without retransmission, and when retransmissions are neededa reduced delay is achieved due to a combined effect of increasedreliability of individual transmissions and reduced round-trip time foreach (re-)transmission. A particular detection algorithm compatible toexisting 3GPP specifications is proposed. Autonomous UE switchingbetween short (according to the invention) and long (according to priorart) TTI as need be will guarantee backward compatibility and RRCsignaling reception.

FIG. 4 illustrates a preferred channel structure according to theinvention. Compared to prior art channel structure, as illustrated inFIG. 3, a radio frame according to the preferred embodiment of theinvention is divided into an integer number of equally sized sub-frames,each sub-frame comprising an integer number of slots. Exemplary 15 slotsper frame, in accordance with 3GPP technical specifications, can befactored, giving three possible sub-frame sizes of 3 or 5 slotsrespectively. According to the invention a preferred sub-frame sizecomprises 3 slots, i.e. there are 5 sub-frames of a radio frame, eachsub-frame having a duration of 10/5=2 ms. Of course, unequally sizedsub-frames of a radio frame is also a possibility, however lesspreferred.

Both DPDCH and DPCCH are divided into the sub-frame structure. Withpreferred 5 sub-frames there are consequently 5 data blocks, <<Data#0>>, <<Data #1>>, <<Data #2>>, <<Data #3>>, <<Data #4>>.

According to the preferred embodiment TFCI of the sub-frame channelstructure, TFCI_(sf), is included in every transmitted sub-frame ofDPCCH. In an alternative embodiment, there is only needed to transmitTFCI_(sf), at TFCI_(sf) changes. However, as such changes may occur forevery sub-frame the sub-frame channel structure allows for at least oneTFCI_(sf) in each sub-frame, <<TFCI_(sf) #0>>, <<TFC_(sf) #1>>,<<TFCI_(sf) #2>>, <<TFCI_(sf) #3>>, <<TFCI_(sf) #4>>.

The blind TTI detection according to the invention may be used withknown technologies of TFCI detection according to 3GPP technicalspecification.

The TFCI field of the slot structure according to 3GPP technicalspecifications comprises two bits per slot. For TTI being an integermultiple of a radio frame, TFCIrf consequently comprises 15·2=30 bits.The TFCI_(rf) bits are FEC encoded such that the 30 bits represent 10information bits. I.e., 1024 transport format combinations can berepresented by TFCI_(rf). For the example of sub-frames comprising threeslots, TFCI_(sf) would comprise 6 bits, given that two bits of each slotcarry TFCI bits. Depending on FEC coding, these TFCI bits wouldrepresent at most 64 transport format combinations. With redundancyincluded, typically 4 or 8 transport format combinations can berepresented. Circumventing need for spending TFCI bits on explicitsignaling of TTI allows maximal flexibility of transport formats. FIG. 6shows a flow chart schematically illustrating detection according to apreferred embodiment of the invention.

The receiver initially anticipates received TFCI field comprisesTFCI_(sf) data and detects, by decoding of the first slots on DPDCHcorresponding to a first sub-frame, if any, whether or not there is asub-frame of the received transmission. Each data channel sub-frame isprotected by forward error control coding. This enables the receiver tocorrect and/or detect transmission errors. Only some symbol combinationsare valid codewords. If a symbol combination is not among the consideredcorrect codewords after decoding a transmission error can be detected.However, if e.g. a radio frame codeword, not comprising a sub-framecodeword in its first slots, is transmitted this will appear as atransmission subject to transmission errors to a decoder assuming asub-frame codeword being transmitted. This relationship is utilized inthe preferred embodiment of the receiver operating according to the flowchart of FIG. 6 for determining whether or not a sub-frame structure issuperimposed on the prior art radio frame structure.

If decoding is successful, it is a great probability for a superimposedsub-frame structure and the decoded sequence is accepted as a validcodeword. Data transmitted in the sub-frame on DPDCH (see FIG. 4) isdecoded using TFCI_(sf) information and forwarded to higher layers. Oncea sub-frame structure is detected the decoding continues for allsub-frames of the radio frame. After the last sub-frame of the radioframe, the process is halted for that radio frame. The process isrepeated for next received one or more radio frames.

However, if the initially assumed sub-frame on DPDCH is not successfullydecoded and not all assumed sub-frames have been decoded, the initialassumption of a superimposed sub-frame structure on the transmission isrejected and a radio frame structure according to prior art is assumed.This assumption is investigated by decoding entire TTI assuming receivedTFCI relates to TFCI_(rf) data of radio frame structured transmission onDPDCH and, if DPDCH decoding is successful, decoding one or more DPDCHradio frames for a transmission time interval as indicated by TFCI. IfTTI is one radio frame, once the DPDCH radio frame is decoded it isforwarded to higher layers and the decoding process halted and restartedfor the next one or more radio frames. If TTI is greater than one radioframe, the entire TTI on DPDCH is decoded and forwarded to higher layersprior to halting the process and restarting for next one or more radioframes. Otherwise, no more data is passed to higher layers and theprocess ends to restart for next one or more radio frames.

By decoding all radio frames of a transmission time interval, when thereis no sub-frame structure superimposed, prior to restarting the processfor next one or more radio frames an advantage of speeding up thedecoding is achieved as sub-frame decoding can then be omitted.

According to a second embodiment, the sub-frame and radio frame decodingare non-exclusive. This is illustrated in FIG. 7 reflected in thatcondition <<End of radio frame?>> of FIG. 6 is excluded and step<<Decode radio frame TFCI_(rf)>> entered unconditionally when allsub-frames of a radio frame have been candidate decoded. The outcomes ofdecoding sub-frames and entire radio frame, respectively, are weightedand compared and the outcome (entire radio frame or one or moresub-frames) with greatest likelihood of being correct is selected instep <<Select higher layers candidates; forward to higher layers>>. Onesuch comparison would be to select between whether or not a sub-framechannel structure is superimposed depending on, which of thealternatives would correspond to the smallest number of transmissionerrors. In FIG. 7, TTI comprising a plurality of radio frames does notinclude candidate(s) selection for more than first radio frame. However,more radio frames of TTI could be included at the expense of increasedbuffering. When a radio frame is TFCI detected only one radio frame (thefirst) of TTI is required to be detected.

According to a third embodiment a majority vote on the sub-framedecoding attempts of a received radio frame is determined prior to anydecoding attempt of an entire radio frame. If, e.g., 3-5 out of 5sub-frames are correctly decoded, transmissions are considered accordingto a sub-frame structure. Depending on false alarm rate and miss ratethe vote threshold may be adjusted, e.g. requiring 4-5 correctly decodedsub-frames for considering data sent according to the sub-framestructure.

The preferred, second and third embodiments described above may bereferred to as blind detection. However, it should be noted thataccording to the invention only TTI detection is blind. Once TTI isdetermined, TFCI_(rf) and TFCI_(sf), respectively, is used to inform thereceiver on control information, e.g. code rate.

On the transmitting side the terminal preferably decides whether or notto make use of the sub-frame channel structure according to needs andradio environment. The decision is based on one or more aspects such asavailable transmit power, transmission activity on channels requiringradio frame channel structure without sub-frame channel structure.

As an alternative to blindly detecting whether a sub-frame structure issuperimposed or not, this could be signaled through differences betweenTFCI_(rf) and TFCI_(sf). To achieve sufficiently high reliability, therea distance measure is considered. The greater the distance, the greaterthe reliability. The smallest distance between any TFCI and anyTFCI_(sf) is determined in terms of number of differing positions. Twonon-exclusive alternatives for increasing the distance beyond what TFCIfield according to prior art alone allows for are considered:

-   -   The distance is increased by utilizing bits of slot FBI-field        for TFCI_(sf).    -   The distance is increased by using different pilot sequences        depending on whether or not a sub-frame structure is imposed or        not.

As an alternative, the above-mentioned increase of TFCI_(sf) field sizecould, wholly or partially, be used for allowing more transport formatcombinations, at the expense of a smaller distance increase.

Irrespective of which method is used for detection (blind detection orTFCI difference), each received sub-frame is preferably acknowledged(positively or negatively) by the receiver, when a sub-frame structureis superimposed. A transmitter of an earlier release will simply ignoresuch unknown acknowledgments.

A problem related to hybrid ARQ, combining subsequent decodings forincreased reliability causes another problem related to the superimposedsub-frame structure. According to the preferred embodiment, need fordual buffers to store also a superimposed sub-frame structure, withcapacity of changing the decision until all sub-frames of a radio frameis received, is eliminated. Due to great reliability of the errordetecting code, and the preferred constant sub-frame size of allsub-frames of a radio frame, the decision is made on DPDCH data from thefirst sub-frame. If this sub-frame is indicated to be a valid codeword,the sub-frame structure is anticipated to hold for the entire radioframe and the hybrid ARQ buffer(s) reserved for sub-frame combining. Thedrawback of this solution is obviously that an erroneous decision basedon only one sub-frame could ruin an entire radio frame, if there is nosub-frame channel structure of the transmission.

An alternative solution to this problem is to only allow soft combiningof consecutive transmissions for sub-frame TTIs, excluding TTIs beinginteger multiples of the duration of a radio frame for hybrid.ARQ. Forreasons of symmetry, buffer savings could alternatively be achieved byonly allowing hybrid ARQ for TTIs being integer multiples of a radioframe. A drawback of both these alternative solutions is that ifretransmission of data need to occur without possibility to retransmitusing a sub-frame channel structure, retransmissions cannot be softlycombined. This may be the case e.g. due to mobility (some Nodes B maynot have implemented a sub-frame channel structure or UE is strictlypower limited if moved close to cell border).

L2 MAC layer can request retransmission of transmission units receivedin error. Preferably hybrid ARQ, utilizing information available fromearlier transmission(s) of a transmission unit by proper combining withthe latest retransmission, is used prior to an L2 MAC layer request forretransmission.

At the receiving end, error detection is also performed by layer L2 RLCof FIG. 8. If an RLC protocol data unit, PDU, is received in error orthe PDU is missing, it will be requested for retransmission at a pointin time when a status report is established by the RLC layer. RLC PDUsare transferred to/from the MAC layer SDUs. The MAC SDU possiblyincludes a header not included in the RLC PDU. A network layer PDU or L3PDU can comprise several RLC PDUs, as illustrated in FIG. 8. RLC PDUsare reassembled into RLC service data units, RLC SDU, prior to deliveryto higher layer PDU. The L3 protocol can be, e.g., the InternetProtocol, IP. Upon reception from L3, RLC SDUs are segmented into RLCPDUS.

One reason for terminating the Fast Hybrid ARQ in Node B, as illustratedin FIG. 1 is the reduction of roundtrip delay as compared to terminatingit in RNC. Another reason is that Node B is capable of using softcombining of multiply transmitted data packets, whereas RNC generallyonly receives hard-quantized bits.

Preferably, all Nodes B and UEs of the radio communications systemoperate according to the invention for outstanding performance. However,the invention can also be used in systems also including Nodes B notoperating according to the invention.

A person skilled in the art readily understands that the receiver andtransmitter properties of a BS or a UE are general in nature. The use ofconcepts such as BS, UE or RNC within this patent application is notintended to limit the invention only to devices associated with theseacronyms. It concerns all devices operating correspondingly, or beingobvious to adapt thereto by a person skilled in the art, in relation tothe invention. As an explicit non-exclusive example the inventionrelates to mobile stations without a subscriber identity module, SIM, aswell as user equipment including one or more SIMs. Further, protocolsand layers are referred to in close relation with UMTS terminology.However, this does not exclude applicability of the invention in othersystems with other protocols and layers of similar functionality.

The invention is not intended to be limited only to the embodimentsdescribed in detail above. Changes and modifications may be made withoutdeparting from the invention. It covers all modifications within thescope of the following claims.

1. A method of transmitting data according to a sub-frame channelstructure wherein, for a radio frame channel structure of a data channeland a control channel, said method comprises the steps of: a firsttransmission time interval being an integer multiple of the duration ofa radio frame; and, a second transmission time interval smaller than thefirst transmission interval and corresponding to the duration of asub-frame are defined wherein the sub-frame channel structure is appliedwith the second transmission time interval on the same data channel forwhich the first transmission time interval may be applied, allowing thefirst and second transmission time intervals to interchange fordifferent radio frames of the same data channel.
 2. The method accordingto claim 1, wherein said sub-frame channel structure is superimposed onthe radio frame channel structure.
 3. The method according to claim 1,wherein said transmission time interval is changed without transmittingexplicit control signaling, comprising information on second timeinterval, on the control channel.
 4. The method according to claim 1,wherein said transport format combination information according to thesub-frame channel structure is transmitted if transport formatcombination information has been changed since most recentlytransmission time interval and is not transmitted if transport formatcombination information has not changed.
 5. The method according toclaim 1, wherein symbol intervals corresponding to symbol intervals ofslots representing transport format combination information according tothe radio frame channel structure are representing transport formatcombination information according to the sub-frame channel structure. 6.The method according to claim 1, wherein one or more symbol intervals offeedback information or pilot sequence of one or more radio framechannel structure slots are reallocated to represent transport formatcombination information on the sub-frame channel structure.
 7. Themethod according to claim 1, wherein received sub-frames areacknowledged to data transmitter.
 8. A method of detecting a sub-framechannel structure transmission time interval, comprising the steps of:for a data channel, one or more slots corresponding to a transmissiontime interval of a sub-frame channel structure are received and, for acontrol channel, one or more transmission format control symbols of theone or more slots corresponding to those of the data channel arereceived; and, a candidate decoding of a first data channel sub-frame isperformed assuming transport format control information being inaccordance with the transport format control information of acorresponding control channel sub-frame of the sub-frame channelstructure.
 9. The method according to claim 8, wherein said methodallows detection of inter-change of first and second transmission timeintervals for different radio frames of the same data channel, thesecond transmission time interval corresponding to the duration of asub-frame and being smaller than the first transmission time interval.10. The method according to claim 8, wherein the sub-frame channelstructure transmission time interval is detected without transmiffingexplicit control signaling, comprising information on second timeinterval, on the control channel.
 11. The method according to claim 8,wherein candidate decoded sub-frame data is stored.
 12. The methodaccording to claim 11, wherein all sub-frames of a radio frame arecandidate decoded.
 13. The method according to claim 8, wherein whensaid one or more sub-frames of a radio frame have been candidatedecoded, for the data channel the radio frame is candidate decodedassuming transport format control information being in accordance withtransport format control information of a corresponding control channelradio frame of the radio frame channel structure.
 14. The methodaccording to claim 8, wherein, depending on the outcome of the candidateone or more decodings, for the data channel a transmitted radio frame isselected according to a metric or cost function.
 15. The methodaccording to claim 14, wherein the metric or cost function reflectsprobability of selected data being transmitted.
 16. The method accordingto claim 14, wherein the metric or cost function reflects probability ofdecoded data conditioned by received data.
 17. The method according toclaim 14, wherein the metric or cost function reflects a fraction ofsuccessfully decoded sub-frames of a radio frame.
 18. The methodaccording to claim 17, wherein the fractional metric or cost function isa majority vote.
 19. The method according to claim 14, wherein if datais considered to be radio frame structured data and not being sub-framestructured, transmission time interval is determined from transportformat combination information according to the radio frame structure,and if transmission time interval is greater than radio frame duration,remaining one or more radio frames of the transmission time interval arereceived and decoded according to the radio frame channel structure. 20.The method according to claim 19, wherein no candidate decoding assuminga sub- frame channel structure are undertaken for the remaining radioframes of the transmission time interval.
 21. The method according toclaim 8, wherein if the sub-frame candidate decoding of the data channelsub-frame is successful, candidate decoded sub-frame data is forwardedto higher layers.
 22. The method according to claim 21, whereinsubsequent sub-frames of a radio frame are candidate decoded untilcandidate decoding of a sub- frame fails or all sub-frames of receivedradio frame have been decoded.
 23. The method according to claim 22,wherein failed decoding indicating candidate decoded data not beingvalid data of a sub-frame according to the sub-frame channel structure.24. The method according to claim 8, wherein if the sub-frame candidatedecoding of the data channel sub-frame is unsuccessful, for the datachannel the radio frame is candidate decoded assuming transport formatcontrol information being in accordance with transport format controlinformation of a corresponding control channel radio frame of the radioframe channel structure.
 25. The method according to claim 24, whereinif candidate decoding of radio frame structured data and not beingassumed sub-frame structured, transmission time interval is determinedfrom transport format combination information according to the radioframe structure.
 26. The method according to claim 25, wherein iftransmission time interval is greater than radio frame duration,remaining one or more radio frames of the transmission time interval arereceived and decoded according to the radio frame channel structure. 27.The method according to claim 26, wherein no candidate decoding assuminga sub-frame channel structure is performed for the remaining radioframes of the transmission time interval.
 28. The method according toclaim 26, wherein decoded data is forwarded to higher layers.
 29. Asignal format for transmission of data and control signaling, whereinthe signal format comprises a radio frame structure and a superimposedsub-frame structure, the radio frame being of a first duration and thesub-frame being of a second duration shorter than the first duration,the data part comprising information sufficient for determining whetheror not transmissions are according to the superimposed sub-framestructure; wherein the sub-frame structure comprises transport formatcontrol information if the information has chancjed from an earliertransmission time interval, corresponding to the second duration or aninteger multiple of the first duration.
 30. The signal format accordingto claim 29, wherein the data and control signaling is transmitted on adata channel and control channel respectively.